automount is a daemon that automatically mounts network filesystems when they are first accessed and later unmounts them when they are idle.

automount creates a virtual filesystem mounted at one or more places in the client’s file and directory hierarchy. Potential server mount points within this virtual filesystem appear as symbolic links. Reading a sym- bolic link causes automount to mount the associated remote filesystem in a separate hierarchy and to return the path to the real mount point as the target of the symlink.

To make the “trigger” symbolic links used by automount distinguishable from normal symbolic links, the sticky bit is set in the mode flags for the link. Programs which would normally traverse symbolic links can test for this bit and avoid triggering the mount. Various parts of the sys- tem, including ls(1), have been modified in this way.

Each virtual filesystem created by automount is governed by a correspond- ing map. One or more maps and the location in the hierarchy where they are to appear may be specified on the command line with -m and -mnt:

-m directory map

is followed by a specification of the private mount directory where the actual mounts are to be established:

-mnt actual_root

Each map’s hierarchy is rooted at the directory specified.

FILE MAPS

A map may be file or a special map. A file map is a file containing a list of entries of the form:

location mount_options server:path

mount_options must be a comma-separated list of options drawn from the options known to mount(8) and mount_nfs(8). automount will automatically make available at the map’s mount point the directory specified by server:path (as a symlink). When the symlink is traversed, it will mount the server in the directory specified with -mnt and return the real mount point as the result of the symlink resolution.

SPECIAL MAPS

In addition to reading files specifying mount maps, automount supports the “-fstab”, “-static”, and “-nsl” maps. The “-fstab” and “-static” maps are derived from fstab(5) data (as provided by getfsent(3)).

All mounts in fstab(5) without the “net” option will be made to appear at the fstab(5)-specified location in the form of a symlink into the directory where the “-static” map is actually mounted (itself a direc- tory of symlinks). For example, the entry:

server:/Network/Applications /Network/Applications nfs nosuid 0 0

and automount invocation

automount -m /automount/static -static -mnt /private/var/automount

result in a non-trigger symlink /Network/Applications pointing to /auto- mount/static/Network/Applications which, when traversed, causes server:/Network/Applications to be mounted on /private/var/automount/Net- work/Applications (which would then be returned from reading the link).

All mounts with the “net” option will be mounted within the “-fstab” map’s filesystem using a path of the form:

server/path

For such mounts, the path specified in the fstab(5) entry will be ignored. For example, if the fstab(5) database contained an entry for

polaris:/Library/Fonts

and automount was started as follows:

automount -m /Useful -fstab -mnt /private/Useful

then a symlink would appear in /Useful, /Useful/polaris/Library/Fonts, and link to /private/Useful/polaris/Library/Fonts where the filesystem is actually mounted when the symlink is traversed.

Accessing servers in the NSL hierarchy may prompt the user for authenti- cation.

OPTIONS

-V Print version and host information, then quit

-m directory map Associate the specified map with the given directory. The direc- tory will be created if it doesn’t exist. map may be the name of a file, or it may be the name of a special map. See the FILE MAPS and SPECIAL MAPS sections above.

-d Run automount in debug mode. The program remains in the fore- ground and sends debugging information to standard output.

-1 (The numeric digit “one”.) Modifies the “-fstab” and “-static” maps to do mounts “one at a time”, when an actual mount point is traversed rather than mounting all mounts from a given server when the first of its mounts is referenced and mounted.

-tm secs Set the timeout for NFS mounts to secs seconds. The default value is 20 seconds. The “mnttimeo=n” mount option overrides this default.

-tl secs Set the time-to-live for NFS mounts to secs seconds. The default value is 3600 seconds. The “ttl=n” mount option overrides this default.

automount periodically checks all its mounted filesystems. If it finds any filesystems that have been idle for their associated time-to-live value, it will attempt to unmount them. An unmount will only be successful if there are no processes with open files in that filesystem. Unless -1 is specified, if one or more mounts from a given server are found to be active, any mounts from that server that were successfully unmounted will be immea- diately remounted.

Supplying a ttl value of 0 will disable this behavior and allow servers to remain mounted forever.

-s Force all mounts at startup and never expire any mounts.

-tcp Mount servers using TCP if possible, otherwise using UDP (the default is to try UDP first, then TCP). Per mount_nfs(8), “-T”, “TCP”, or “tcp” mount options have the same effect as specifying -tcp; “-U”, “UDP”, or “udp” mount options force the default behavior of trying UDP first even if -tcp is specified.